1. Field of the Invention
The present invention relates to an ink jet recording apparatus and an ink suction method of the recording head.
Specifically, the present invention relates to an ink jet recording apparatus provided with a recording head which is moved in the direction of the width of a recording paper for printing an image on the recording paper by jetting an ink droplet toward the recording paper based upon print data, and more particularly relates to an ink jet recording apparatus wherein ink is prevented from being dry and being clogged by forming the capping device so that the capping device has a specific structure, the printing of a dot is never omitted and color mixture and mottled color are prevented in color printing, and an ink suction method of the recording head in flushing and cleaning.
2. Description of the Related Art
As graphic processing can be relatively easily executed owing to the development of a personal computer, a recording apparatus which enables the output of a high quality hard copy of a color image on a display is desired.
A recording apparatus in which an ink jet recording head is mounted to meet such a request is provided.
As in such an ink jet recording apparatus, noise in printing is relatively small and a small dot can be formed in high density, it is used for multiple types of printing including color printing.
Such an ink jet recording apparatus is provided with an ink jet recording head to which ink is supplied from ink storage means and paper feed means for relatively moving recording paper to the recording head so as to record by jetting an ink droplet on recording paper, moving the recording head according to a printing signal and forming dots.
A recording head which enables the jetting of black, yellow, cyan and magenta ink is provided to a common head holder and enables not only the printing of a text by black ink but full color printing by changing the ratio in which each ink is jetted. As such an ink jet recording head prints by jetting ink pressurized in a pressure generating chamber on recording paper from a nozzle as an ink droplet, there is a problem that a nozzle aperture is clogged due to the increase of the viscosity of ink and the solidification of ink respectively caused by the evaporation of a solvent from a nozzle aperture, the adhesion of dust, further, the mixture of a bubble and others and as a result, the failure of printing occurs.
Therefore, an ink jet recording apparatus is normally provided with a capping device for sealing a nozzle aperture of the recording head while the ink jet recording apparatus is not used and cleaning means for cleaning a nozzle plate if necessary.
The capping device not only functions as a cap for preventing ink from being dry at a nozzle aperture but is provided with a function for sealing a nozzle plate by a cap member, sucking ink from a nozzle aperture by negative pressure from a suction pump and solving the clogging of the nozzle aperture if the nozzle aperture is clogged.
Processing for compulsorily exhausting ink executed to solve the clogging of a recording head is normally called cleaning, is executed in case printing is restarted after longtime cessation and in case a user presses a cleaning switch to solve the clogging of a recording head and is processing for wiping by a cleaning member formed of an elastic plate such as rubber after an ink droplet is jetted.
A function for applying a driving signal not related to printing to a recording head so as to jet an ink droplet is also provided, is normally called flushing and is operation executed every fixed cycle to recover an uneven meniscus in the vicinity of a nozzle aperture of a head by wiping and others in cleaning and to prevent a nozzle aperture which hardly jets an ink droplet in printing from being clogged.
FIG. 12 is a sectional view showing the schematic constitution of a capping device used for a conventional type ink jet recording apparatus and shows a state in which ink is sucked from a recording head by a cap unit constituting the capping device. FIG. 13 shows a state of the cap unit when it is viewed from the top.
A cap unit 38 is constituted by a rectangular cap case 40 the top face of which is open and a cap member 16 housed in the cap case 40 and formed of flexible material and the cap member 16 is formed with the upper edge slightly protruded from the cap case 40.
An ink absorber 17 formed by porous material is housed at the inner bottom of the cap member 16.
An ink suction port 18 and an atmospheric air open port 19 in most apparatuses are arranged through the cap case 40 and the cap member 16 at the bottom of the cap case 40 and the cap member 16.
The above ink suction port 18 and the atmospheric air open port 19 are arranged so that they are located at a predetermined interval approximately along the center in the longitudinal direction of the capping device when the capping device is viewed from the top as shown in FIG. 13.
In the meantime, a reference number 8 denotes a recording head for color, the recording head 8 is located over the capping device and a nozzle plate 14 is capped by the capping device.
A nozzle aperture 15 is arranged in the nozzle plate 14 and is constituted so that yellow, cyan and magenta ink is jetted by the action of a piezoelectric vibrator 13 arranged corresponding to each nozzle aperture 15.
In the above constitution, ink suction action for solving the clogging of a nozzle aperture is executed by operating a suction pump connected to the ink suction port 18 of the cap member with the cap member 16 closely touched to the nozzle plate 14 of the recording head 8 as shown in FIG. 12 and applying negative pressure to the inside of the cap.
Ink is jetted from the nozzle aperture 15, the atmospheric air flows in from the atmospheric air open port 19 when negative pressure inside the cap is reduced to some extent and negative pressure inside the cap is all released.
However, in the conventional type constitution shown in FIGS. 12 and 13, as the atmospheric air open port 19 is provided under the cap, ink is left at the end of the atmospheric air open port 19 after ink is sucked.
Further, as a sheet formed of porous material is normally used for the ink absorber 17 provided inside the cap, ink bubbles are blown up because opening to the atmospheric air is executed through such an ink absorber.
When such ink bubbles are scattered and adhere to the nozzle aperture 15, color mixture and the failure of printing in a dot occur.
To solve such problems, technique disclosed in Japanese Patent Publication No. Hei. 7-68766 for example for elastically deforming a cap by minutely moving a carriage on which a recording head is mounted or pulling the cap and executing opening to the atmospheric air from clearance made between a nozzle plate and the cap or technique for providing an atmospheric air open port on the surface of the nozzle plate of a recording head and executing opening to the atmospheric air from the side of the head is proposed.
However, as for the former technique, fatigue, distortion and others may occur in cap material due to long-term reciprocation, adhesion between a cap and a nozzle plate may be lost and the reliability of an apparatus is deteriorated.
Also, as for the latter technique, as a head is large-sized by providing an atmospheric air open port on the surface of a nozzle plate and a cap itself is further large-sized, there occurs a problem that the efficiency of suction is deteriorated.
As in a recent ink jet recording apparatus, the number of nozzle apertures constituting a recording head is increased to meet a request for high speed printing and high quality of color printing and as a result, the recording head has a tendency to be large-sized.
Therefore, a cap unit of a capping device for sealing the recording head is also necessarily large-sized, large unbalance occurs in negative pressure to act because of the increase of distance between the ink suction port 18 communicating with a suction pump and the nozzle aperture 15 and ink is difficult to uniformly jet from all nozzle apertures constituting the recording head.
To partly solve such problems, a flow regulating plate for positively changing the resistance of a passage for leading exhausted ink corresponding to distance from an ink suction port is inserted as disclosed in Japanese Patent Publication No. Hei. 7-195712 for example and to promptly and securely exhaust ink into a cap member outside without scattering ink, a capping device provided with an atmospheric air communicating hole disclosed in Japanese Patent Publication No. Hei. 7-290723 and others are proposed, however, as these are provided to securely exhaust ink into a large-sized capping device outside and negative pressure to act on a nozzle aperture cannot be adjusted, ink cannot be uniformly jetted from any nozzle aperture and there is still left a problem that the mottled color and color mixture of printing caused by the above uneven jetting cannot be completely avoided.